1. Field of the Invention
This invention relates to a non-crystalline substance having an optical memory effect which consists of As and Se as the main ingredients, and the additional third component(s), Zn, Au or Ag and/or Cu.
2. Description of the Prior Art
Conventional optical memory substances include non-crystalline chalcogenides such as Ge--As--Te, Ge--S--Sb--Te, As--S--I, etc. It is well known that the optical properties of these substances such as the transmittance, refractive index, reflectivity, etc., vary upon irradiation with a laser beam and thus these substances are suitable for use in optical memory devices. These conventional substances are characterized by their high memory density, i.e., more than 10.sup.7 bit/cm.sup.2, and high reading efficiency. They do not require any processing operations including development, fixing, etc. Further, they have reversibility and thus memory erasing and writing may freely be effected in these substances, a substantial merit thereof.
However, in the Ge--As--Te system, the transmission range falls only in the infra-red region, and thus there exist some defects in operation (limitation on the type of irradiation which can be used, i.e., only infrared irradiation) and detection (the method of detecting infrared radiation must be considered during reading the optical memory device). Further, a high power laser beam is required during use.
With respect to the As--S--I system, the weather resistance thereof is poor and thus the surface of the substance is apt to be deteriorated with the passage of time.
On the other hand, in the Ge--As--Te system the yield point is high, i.e., Tg (transmittance) is high. Accordingly, if the transmittance is to be changed depending upon the light used, a high power laser beam is required. This is not preferred from an economical point of view and, further, the use thereof is limited, i.e., high power laser apparatus is mandatory.